1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an electrophotographic image forming apparatus having a detachable developer cartridge.
2. Description of the Related Art
An electrophotographic image forming apparatus produces an image by forming an electrostatic latent image, corresponding to a desired image, by scanning light onto a photosensitive medium charged to a uniform electrostatic potential. Then, the latent image is developed by providing toner thereto and the image developed on the photosensitive medium is transferred to a sheet of printing paper either directly or indirectly. Lastly, the transferred image is fused by applying heat and pressure thereto.
The electrophotographic image forming apparatus includes a developer cartridge containing a photosensitive medium and toner. The developer cartridge is replaced when the service life of the cartridge ends. Therefore, the developer cartridge is detachably installed on the main body of the image forming apparatus. Once the developer cartridge is installed, the cartridge has to be fixed tightly at a predetermined position.
Conventional printers employ a coupler driven by a drive motor to fix the developer cartridge to the main body. When the developer cartridge separates, the coupler is moved back to avoid interference with the installed developer cartridge. After the developer cartridge is installed and a door is closed, the drive motor is rotated. The coupler is advanced and coupled with one end of a photoreceptor drum. Accordingly, the replaced developer cartridge is fixed at a predetermined position. When the door is opened to detach the developer cartridge, the drive motor rotates in an opposite direction and the coupler moves back and separates from one end of the photoreceptor drum.
In the above described method of fixing a developer cartridge using a drive motor, when the supply of electricity is interrupted, for example, when a power supply unit of a main body of the image forming apparatus malfunctions, the coupler cannot move backwards; therefore, detachment of the developer cartridge from the apparatus is prevented.
Furthermore, in conventional printers, the coupler and one end of the photoreceptor drum have complementary shapes. Thus, if the developer cartridge is not installed properly, the coupler and one end of the photoreceptor drum cannot be coupled together. Consequently, the installation of the developer cartridge is obstructed.
Accordingly, there is a need for an improved electrophotographic image forming apparatus in which a developer cartridge can be fixed and detached independently of a drive motor.